1. Field of the Invention
This invention is in the field of separating non-ferrous metals from secondary substances which are waste products in steel manufacture, the method being carried out within the framework of a sintering process wherein the secondary substances are employed as part of a fill which contains at least one mixture of a secondary substance and a regular sinterable mixture in the form of layers. The non-ferrous metals are volatilized and recovered as dust for return to the sintering operation.
2. Description of the Prior Art
A method for separating non-ferrous metals, particularly lead and zinc, from such secondary substances is disclosed in our German Patent application P No. 30 42 941, corresponding to U.S. Ser. No. 319,939, filed Nov. 10, 1981 of which this application is a continuation-in-part. As described in the prior application, a mixture containing such secondary substance and a normal sintering mixture are introduced into a sintering process in the form of layers. The layer consisting of pre-sintered material is disposed at the bottom, that is, directly adjacent to the sintering grate. This lowermost layer serves for the thermal protection of the sintering grate. Next, there is a layer which contains, among other things, the secondary substances and a further layer which consists of a normal sintering mixture. Gas extraction hoods are situated below the sintering grate so that an ignition process initiated in the uppermost layer propagates through the fill and the exhaust gases are withdrawn downwardly. The gas extraction hoods are combined with one another at the exhaust gas side such that there is one group connected to a blower and a second group connected to a different blower. The combination of gas extraction hoods on the exhaust gas side is designed in conjunction with the conveying speed of the sintering grate, the thickness of the material placed on the grate, as well as the propagation speed of the ignition front traversing the fill from top to bottom such that the ignition front reaches the layer carrying the secondary substances at the time at which the fill has arrived at the inlet area of the second group of gas extraction hoods. The possibility is thus created of achieving conditions necessary for lead and zinc separation by means of changing the temperature and pressure conditions in the gas extraction hoods of the second group, in conjunction with the use of a fuel excess in the layer carrying the secondary substances.
The non-ferrous metals predominantly consisting of oxides of lead and zinc are thereby reduced, volatilized, discharged as a gaseous phase, and are substantially reoxidized and collected as dust by means of a gas filter.